(1) Field of the Invention
The present invention relates to a gravel-or-the-like removing device which can discharge gravel, sand, mud or the like in a dredging site, a civil engineering work site, a sewage treatment plant, a sedimentation pool or a pit within a plant, an inside of a manhole or the like to a given place. In this specification, the term “gravel-or-the-like” means not only gravel but also sand, gravel, mud and the like.
(2) Description of the Related Art
Conventionally, as a gravel-or-the-like removing device which is served for the above-mentioned usage, there exists a suction pump 150 which has a constitution shown in FIG. 15, for example. This suction pump 150 is substantially comprised of an impeller casing 154 which accommodates an impeller 152 driven by a motor 151 in the inside thereof and includes a suction opening 153 at the center of a lower surface thereof, a perforated cylindrical strainer 155 which has an upper end thereof connected to a lower portion of an impeller casing 154 and a lower end thereof opened downwardly, and an agitator 157 which is mounted on an agitator mounting shaft 156 which is connected to an output shaft of the motor 151.
To explain the gravel or the like removing operation using such a suction pump 150, the impeller 152 and the agitator 157 are integrally rotated upon driving of the motor 151 so that gravel or the like is agitated by the agitator 157, the agitated gravel or the like is sucked into the inside of the impeller casing 154 by the impeller 152, and thereafter, the agitated gravel or the like is discharged to a desired location through a discharge pipe 158.
In the normal operation, at the time of starting the suction pump 150, as a piled level of the gravel or the like S, a level D which is positioned below the cylindrical strainer 155 is assumed. However, there may be a case that the operation of the suction pump 150 is temporarily stopped. In this case, there is a possibility that the gravel-or-the-like piled level exceeds the level D, that is, the gravel-or-the-like piled level reaches a level E.
In such a case, the gravel or the like is filled in the inside of the cylindrical strainer 155 through lateral holes formed in a peripheral wall of the cylindrical strainer 155. On the other hand, since water which gives fluidity to the gravel or the like is not supplied from the outside, the gravel-or-the like suction and discharge operation becomes difficult.
To solve such problems, Japanese Laid-open Patent Publication 30652/1970 proposes a gravel-or-the-like removing device 160 which has a constitution shown in FIG. 16 and FIG. 17.
As shown in the drawing, the gravel-or-the-like removing device 160 is mounted on a bottom surface 161 of a pit A on which the gravel or the like is piled. A suction pump 162 which constitutes a body portion of the gravel-or-the-like removing device 160 includes an impeller casing 164 which forms a gravel-or-the-like suction opening at the center of a lower end thereof and makes a gravel-or-the-like discharge opening formed in a portion of a peripheral wall thereof communicably connected to a discharge pipe 163, an impeller 165 which is rotatably accommodated in the inside of the impeller casing 164, and a watertight motor 166 which rotatably drives the impeller 165. A cylindrical strainer portion 168 which has a bottom plate 167 is connected to a bottom portion of the impeller casing 164 in a coaxial manner. A large number of lateral holes 170 and vertical holes 171 are respectively formed in an entire peripheral wall 169 and the entire bottom plate 167 of the cylindrical strainer portion 168. The cylindrical strainer portion 168 having such a constitution is supported on a pump support base 172 which is formed of an annular frame. Further, an agitator 174 is fixedly secured to an agitator mounting shaft 173 which is integrally connected to an output shaft of the watertight motor 166.
Further, a water suction pipe 175 which is vertically arranged in the inside of the pit A has a lower-end opening 176 thereof communicably connected to a portion of the peripheral wall 169 of the cylindrical strainer portion 168 and an upper-end opening 177 thereof provided with a water auction auxiliary strainer 178. Here, as shown in FIG. 17, the lower-end opening 176 of the water suction pipe 175 is communicated with the cylindrical strainer portion 168 at a position below the gravel-or-the-like piled level B. On the other hand, the water suction auxiliary strainer 178 is disposed far above the gravel-or-the-like piled level B and is positioned in the vicinity of a filled water level C.
Due to such a constitution, even when the suction pump is embedded in the gravel or the like, at the time of starting the suction pipe, it becomes possible to supply water outside a gravel-or-the-like piled region which is disposed above the gravel-or-the-like piled level B into the suction pump through the suction pipe so that the gravel or the like can be diluted whereby the gravel or the like suction and discharge operation can be performed smoothly.
However, the above-mentioned gravel-or-the-like removing device 160 has a following task to be solved in an actual operation. That is, as shown in FIG. 16 and FIG. 17, the cylindrical strainer portion 168 has a large number of lateral holes 170 on the entire surface of the peripheral wall 169. Accordingly, when the cylindrical strainer portion 168 is completely embedded in the inside of the gravel or the like during a period in which the operation of the suction pump is stopped, a large volume of gravel or the like which is present along the outer periphery of the peripheral wall 169 is collapsed and enters the inside of the cylindrical strainer portion 168 through these lateral holes 170 so as to fill the inside space of the cylindrical strainer portion 168 with the gravel or the like. When the suction pump is started in such a state, although water is supplied to the inside of the cylindrical strainer portion 168 through the suction pipe 175, a quantity of the gravel or the like which the suction pump intends to suck becomes overwhelmingly large compared to a quantity of water supplied through the suction pipe 175. Accordingly, the concentration of the gravel or the like is still excessively high so that the smooth suction and discharge operation becomes difficult.
The present invention has been made to solve such a problem and it is an object of the present invention to provide a gravel-or-the-like removing device which can surely and efficiently suck and discharge the gravel or the like even when the suction pump is embedded in the inside of the gravel or the like as in the case that the operation of the suction pump is temporarily stopped.